wordcraft/docs/file-format-parity.md

File-format parity with Microsoft Word

Last reviewed: 2026-10-10 · Last updated: 2026-10-10 · Change: major (first version; every format Word reads or writes, measured from the readers and writers on origin/main) · Target: Microsoft Word (Microsoft 365) for Mac 16.113.4, plus Word for Windows' extra formats

Every format Word opens or saves, what WordCraft does with it, and how it's tested. Fidelity is the share of a typical real-world file's content and formatting that survives (read: shows correctly; write: Word opens it showing the same). Summary in target-app-parity.md; the work items are in gaps.md.

Dimension: ~60% (estimated), 185–300 h to full (the sum of the rows below). The weighted table gives ~64%; we discount it to ~60% because DOCX fidelity has never been checked on real-world files. DOCX dominates the weight: a Word user sends and receives .docx; everything else is occasional.

Formats

Weights are the share of a Word user's file traffic (estimate). Read/write: ✅ yes, 🟡 partial, ❌ no, — Word doesn't either.

Format	Weight	Word	WordCraft read	WordCraft write	Fidelity	Hours	How it's tested	Notes
.docx Word Document (ECMA-376 Transitional)	70%	R/W	✅	✅	~65%	70–110	crates/docx/tests (roundtrip 28, fixtures 21, malformed 8, bidi 4, citations 5); synthetic fixtures only	Word opens our files. Untested on a real-world corpus. Details below
.docx Strict Open XML	1%	R/W	✅ (namespace mapping in xml.rs)	❌	~60%	2–4	one fixture	Writing Strict is rare
.docm / .dotx / .dotm	3%	R/W	✅	✅	~65%	incl. above	macro_packages.rs	Macros and signatures kept on save (#172); macros never run
.doc Word 97-2003 (and .dot)	8%	R/W	🟡	❌	~55%	25–40	crates/docbin/src/tests.rs (50)	Spec-based reader ([MS-DOC]): text, formatting, styles, sections, headers/footers, tables, lists, notes, fields, bookmarks, pictures. Metafile (WMF/EMF) pictures, Word 6/95 files and encrypted files are refused or dropped. No writer
PDF export	8%	W	—	✅	~80%	6–10	crates/pdf/src/tests.rs	krilla: embedded subsets, selectable text incl. field results (#133), links, outline, tagging. Fonts it can't subset become outlines (#132). No PDF/A option, no "best for printing/online" choice
PDF open (PDF Reflow, Word for Windows)	1%	R	❌	—	0%	30–50	—	Converting a PDF into an editable document. A sibling app (PdfCraft) may supply the parser
.rtf Rich Text Format	3%	R/W	🟡	🟡	~50%	10–15	crates/formats/src/tests.rs	~1,500 lines: text, character/paragraph formatting, styles, lists, tables, pictures (\shppict, #154), fields, bookmarks. Thin: comments, notes, revisions, sections, RTL
.odt OpenDocument Text	2%	R/W	🟡	🟡	~50%	8–12	crates/formats/src/tests.rs	Styles, lists (#87), tables, pictures, headers/footers, page breaks (#86). No footnotes, comments, tracked changes, fields or RTL
.txt Plain text	2%	R/W	✅	✅	~95%	1–2	unit tests	Encoding detection; Word's encoding choice dialog and line-ending options missing
.htm/.html Web Page and Web Page, Filtered	1%	R/W	🟡	🟡	~60%	6–10	crates/formats/src/tests.rs	Tables (#102), relative pictures embedded (#113), missing </head> tolerated (#154). No Word "Web Page" (with _files folder) round-trip
.mht/.mhtml Single File Web Page	<1%	R/W	❌	❌	0%	3–5	—
.xml Word XML Document (Flat OPC)	<1%	R/W	❌	❌	0%	3–5	—	The DOCX parts in one XML file; cheap once the DOCX code is reused
.xml Word 2003 XML (WordprocessingML 2003)	<1%	R/W	❌	❌	0%	5–8	—	Legacy
.wps Works 6–9, WordPerfect .wpd (Windows)	<1%	R	❌	—	0%	10–20	—	Windows-only converters; low value
Encrypted/password-protected .docx/.doc	1%	R/W	❌	❌	0%	6–10	—	ECMA-376 Agile Encryption; .doc RC4/XOR detected and refused (docbin fib). Issue #55
.md Markdown	—	(no)	✅	✅	—	—	crates/formats/src/tests.rs	Beyond Word
.tex LaTeX	—	—	✅	✅	—	—	crates/formats/src/tests.rs	Beyond Word (#11), incl. math
.png page images	—	(Save as picture, Mac)	—	✅	—	—	io_ext.rs
.json document model	—	—	✅	✅	—	—	engine tests	For agents

DOCX in depth

Measured by grepping crates/docx/src/read and src/write for the OOXML elements (2026-10-10).

Feature	Read	Write	Notes
Text, runs, paragraph and character properties, styles, numbering, sections	✅	✅	Including complex-script props (w:rtl, w:cs, w:szCs, w:bCs…), East Asian fonts kept apart from Latin (#111)
Tables incl. floating (w:tblpPr), table styles and conditional formatting	✅	✅	Custom table styles round-trip (#256)
Headers/footers (first, even/odd), page borders, line numbers, gutter, mirror margins	✅	✅
Footnotes, endnotes, comments	✅	✅	commentsExtended written; commentsIds, modern threaded comments (w16cex) partly
Tracked insertions and deletions (w:ins/w:del), paragraph-mark revisions	✅	✅	#125, #244
Formatting revisions (w:rPrChange, w:pPrChange, w:sectPrChange, w:tblPrChange)	❌	❌	Lost on open. Issue #41
Move tracking (w:moveFrom/w:moveTo)	🟡	❌	Read as plain insert/delete
Fields (w:fldChar, w:fldSimple), TOC, cross-references, ADDIN citations	✅	✅	Field codes Word supports but we don't evaluate keep their cached result
Content controls (w:sdt)	🟡	❌	Content kept, the control (type, binding, placeholder, lock) dropped
Legacy form fields (w:ffData), check boxes, drop-downs	❌	❌
DrawingML pictures inline and anchored (wp:anchor), wrap square/tight/through/top-bottom	✅	✅	Tight/through read and written, laid out as square
DrawingML shapes and text boxes (wps:)	✅	✅	Preset geometries subset
Group shapes (wpg:), drawing canvas	❌	❌	Dropped
VML (w:pict, v:shape, v:textbox)	🟡	❌	Pictures and text boxes, best effort (#242)
Charts (c:chart), SmartArt (dgm), ink, 3D models, OLE objects (w:object)	❌	❌	Dropped on read, not preserved on save. A document with a chart loses it silently
Equations (OMML m:oMath)	✅	✅	#191
Themes, font table, settings, compatibility mode	✅	✅	Embedded fonts (w:embedRegular) not read
Custom XML parts, document properties, bibliography sources	🟡	🟡	Custom properties round-trip; bibliography sources pending (#169)
Ruby, w:eastAsianLayout, w:fitText, document grid (w:docGrid)	❌	❌	East Asian layout
Glossary document (building blocks), w:altChunk, sub-documents	❌	❌
Hostile input	✅	—	malformed.rs, capped allocations, never-crash standard

What decides beta for formats

1. A real-world DOCX corpus opened, rendered and round-tripped, compared page by page with Word (local only: Word output can't be committed; keep a manifest and our own renders).
2. Preserve what we can't render: charts, SmartArt, OLE, ink and content controls survive a round trip (keep the parts and the run), and charts/SmartArt show their fallback picture.
3. Formatting revisions and content controls read and written.
4. Encrypted .docx opens with a password.

Revision history

Date	Change	Summary
2026-10-10	trivial	Custom table styles round-trip (#256 merged)
2026-10-10	major	First version: Word's full format list, read/write status, DOCX element coverage from the source, fidelity and hours